This paper presents a climatology and trends of tropospheric ozone in the
Southwestern Indian Ocean (Reunion Island) and South Africa (Irene and
Johannesburg). This study is based on a multi-instrumental dataset:
PTU-O<sub>3</sub> ozonesondes, DIAL LIDAR and MOZAIC airborne instrumentation.
<br><br>
The seasonal profiles of tropospheric ozone at Reunion Island have been
calculated from two different data sets: ozonesondes and LIDAR. The two
climatological profiles are similar, except in austral summer when the LIDAR
profiles show greater values in the free troposphere, and in the upper
troposphere when the LIDAR profiles show lower values during all seasons.
These results show that the climatological value of LIDAR profiles must be
discussed with care since LIDAR measurements can be performed only under
clear sky conditions, and the upper limit of the profile depends on the
signal strength.
<br><br>
In addition, linear trends have been calculated from ozonesonde data at
Reunion and Irene. Considering the whole tropospheric column, the trend is
slightly positive for Reunion, and more clearly positive for Irene. Trend
calculations have also been made separating the troposphere into three
layers, and separating the dataset into seasons. Results show that the
positive trend for Irene is governed by the lower layer that is affected by
industrial pollution and biomass burning. On the contrary, for Reunion
Island, the strongest trends are observed in the upper troposphere, and in
winter when stratosphere-troposphere exchange is more frequently expected.